1. Field of the Invention
The present invention relates to a process for the monolithic molding of superplastic material by techniques such as superplastic molding and if necessary diffusion bonding using products having three or more layer-structure made up of metal plates such as titanium alloy, to produce the products used for parts that require particular a heat-resistance is required (e.g., body structure of airplane).
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Metals and alloys such as titanium and most of its alloys and nickel alloys have superplasticity characteristics. For instance, it is known that titanium alloys having appropriate compositions provide elongation of 300%. The superplastic materials can be rather easily molded using a superplastic molding process to provide products having even extremely complicated shape.
A process for monolithic molding of the above superplastic material using techniques of superplastic molding and diffusion bonding, is concretely explained with reference to FIGS. 14 to 17.
As shown in FIG. 14, three metal plates having superplasticity (e.g., titanium sheets) 1, 2 and 3 are provided. In case the sheets 1, 2 and 3 are superposed as indicated in FIG. 15, non-bonding regions 4a and 4b are provided on one side (i.e., surface of the sheet 1 intermediately located between the sheets 2 and 3) and a non-bonding region 5a is provided on the other side such that a part of the non-bonding region 5a is overlapped with parts of the non-bonding regions 4a and 4b as seen on a plane surface. On portions that the non-bonding regions 4a and 4b are overlapped with the non-bonding region 5a as seen on the plane surface, gas holes 6 are provided beforehand respectively, and further a groove for introducing molding gas 7 is formed in contact with one end of the non-bonding region 4a. 
A core-sheet 1, which is the above intermediate metal plate, is put between face sheets 2, 3, which are the above top and bottom metal plates. A hole for feeding molding gas 8 is provided in the face sheet 2. The hole for feeding molding gas 8 is connected to one end of a passage for introducing molding gas, which is formed by the groove for introducing molding gas 7 and the face sheet 2 by superposing the face sheet 2 on the core sheet 1.
An anti-bonding agent 9 (e.g., Yttria) is coated on the non-bonding regions 4a, 4b and 5a of the core sheet 1, and the face sheets 2 and 3 are superposed on both sides of the core sheet 1 to form superposed sheets (laminate) 10 as shown in FIG. 15.
Subsequently, the superposed sheets 10 are set in a molding die 30 consisting of a first molding die 31 and a second molding die 32, and air of a first molding die interior 31A and a second molding die interior 32A is replaced with an inert gas while boundaries 11 and 12 between the core sheet 1 and each of the face sheets 2 and 3 are evacuated. Then the superposed sheets 10 and the molding die 30 are wholly heated to a desired temperature, and an inert gas is introduced into the first molding die interior 31A and the second molding die interior 32A to a desired pressure to diffusively bond the core sheet 1 to bonding regions 13a, 13b, 13c, 14a and 14b of each of the face sheets 2 and 3. Thereafter, the inert gas within the interiors 31A and 32A is discharged.
Then, an inert gas is introduced into the non-bonding region 4a between the core sheet 1 and face sheet 2. The inert gas is fed from a hole for providing molding gas 31a opened on the first molding die 31 through the hole for feeding molding gas 8 and the groove for introducing molding gas 7. The inert gas introduced into the non-bonding region 4a having the anti-bonding agent 9 brings about superplastic deformation of the core sheet 1 and the face sheets 2 and 3 in the region corresponding to the non-bonding region 4a. Thereby the portions corresponding to the region 4a of these sheets are expanded to form a first enlarged room 15a. On the other hand, an inert gas is introduced into the non-bonding region 5a having the anti-bonding agent 9 through the gas hole 6, and consequently the core sheet 1 and the face sheets 2 and 3 are superplastically deformed in the region corresponding to the non-bonding region 5a to form a second enlarged room 15b. 
Subsequently, the inert gas introduced into the second enlarged room 15b is further introduced into the non-bonding region 4b having the anti-bonding agent 9 through the gas hole 6, and consequently the core sheet 1 and the face sheets 2 and 3 in the region corresponding to the non-bonding region 4b are superplastically deformed to form a third enlarged room 15c. Thus, as shown in FIG. 17, the inert gas is introduced until the face sheet 2 is pressed to be contacted with a molding surface 31b of the first molding die 31 and the face sheet 3 is also pressed to be contacted with a molding surface 32b of the second molding die 32, and hence a product having a shape whose periphery reflects the molding surface 31b of the first molding die 31 and the molding surface 32b of the second molding die 32 is obtained.
The above-mentioned process for the monolithic molding of molding material using techniques such as superplastic molding and diffusion bonding, the technique comprising superposing plural titanium alloy sheets on which an anti-bonding agent is coated and introducing an inert gas into a molding die interior, is described in for example JP-A11-169977.
According to the prior art described above, constituent materials are superplastically molded and diffusively bonded to each other to be monolithically molded. Hence, even a product having a complicated shape can be rather easily molded, which results in simplification of process procedures and reduction of production cost as well as high strength of product.
In the above superplastic molding, though a core sheet 1 is mainly superplastically deformed to provide a desired molded product, face sheets 2 and 3 putting the core sheet therebetween are also deformed during superplastic deformation of the core sheet due to their superpasticity. In the deformation, the face sheets are influenced especially by pressure introduced in non-bonding regions 4a and 4b, and hence, as shown in FIG. 18, portions corresponding to enlarged rooms 15a, 15b and 15c of the face sheets 2 and 3 are forced to expand whereby local expansions are generated in the portions corresponding to the enlarged rooms 15a, 15b and 15c of the face sheets 2 and 3. The local expansions occasionally cause wrinkles on the molded product.
The local expansions of the face sheets 2 and 3 can be avoided by an increase of thickness of the face sheets. However, the multi-layer hollow products obtained in the above techniques are desired to be light, and therefore the increased the thickness requires additional processing for reducing thickness of the face sheets 2 and 3 after the molding process. Further the yield of the products may reduce to increase the production cost.
In view of the above-mentioned problems, an object of the invention is to provide a process for the monolithic molding of superplastic material wherein generation of wrinkles on the molded product can be prevented by avoiding local expansion generated in the no-bonding regions of both sides (top and bottom sides) of three or more metal sheets (metal plates) when the metal plates are monolithically molded by means of superplastic molding.
The present invention to attain the object is provided by a process for the monolithic molding of superplastic material comprising the steps of:
providing at least three metal plates capable of superplastic molding and diffusion bonding,
applying an anti-bonding agent onto regions of the plates to define bonding regions and non-bonding regions on the plates, bonding regions and non-bonding regions provided between the plates,
superposing the metal plates one on another to form superposed plates,
setting the superposed plates in a molding die, and
heating the molding die interior to a molding temperature to diffusively bond superposed portions of the superposed plates to each other, the superposed portions corresponding to the bonding regions, and superplastically molding the metal plates by introducing a gas into the non-bonding regions to apply pressure to the regions;
wherein auxiliary plates for molding are placed on top and bottom sides of the superposed plates through the anti-bonding layer, respectively, the superposed plates and the auxiliary plates are set in the molding die, and a pressure lower than pressure applied to the non-bonding regions is applied to spaces between inner wall of the molding die and the auxiliary plates to control movement of the top and bottom plates whereby the superplastic molding is performed.
According to the above-mentioned invention, the auxiliary plates for molding are placed on top and bottom sides of the superposed plates, the superposed plates and the auxiliary plates are set in the molding die, superposed portions of the superposed plates corresponding to the bonding regions, are diffusively bonded to each other and the superposed plates are superplastically molded by introducing a gas into the non-bonding regions to apply pressure to the regions while a pressure lower than pressure applied to the non-bonding regions is applied to spaces between inner wall of the molding die and the auxiliary plates. Thus, when the top and bottom metal plates of the superposed metals are superplastically molded, deformation of the top and bottom plates is controlled by the auxiliary plates pressed from behind, whereby generation of wrinkles on the molded product can be prevented by avoiding local expansion generated in the non-bonding regions of the metal plates.
Another invention to attain the object is provided by a process for the monolithic molding of superplastic material comprising the steps of:
providing at least three metal plates capable of superplastic molding,
applying an anti-bonding agent onto regions of the plates to define bonding regions and non-bonding regions on the plates, bonding regions and non-bonding regions provided between the plates,
bonding the portions corresponding to the bonding portion of the plates one on another to form superposed plates,
setting the superposed plates in a molding die, and
heating the molding die interior to a molding temperature to superplastically molding the metal plates by introducing a gas into the non-bonding regions to apply pressure to the regions;
wherein auxiliary plates for molding are placed on top and bottom sides of the superposed plates through the anti-bonding layer, respectively, the superposed plates and the auxiliary plates are set in the molding die, and a pressure lower than pressure applied to the non-bonding regions is applied to spaces between inner wall of the molding die and the auxiliary plates to control movement of the top and bottom plates whereby the superplastic molding is performed.
According to the above-mentioned invention, the portions corresponding to the bonding portion of the metal plates are beforehand bonded one on another to form superposed plates, the superposed plates and the auxiliary plates are set in the molding die, superposed portions of the superposed plates are bonded to each other and the superposed plates are superplastically molded by introducing a gas into the non-bonding regions to apply pressure to the regions while a pressure lower than pressure applied to the non-bonding regions is applied to spaces between inner wall of the molding die and the auxiliary plates. Thus, when the top and bottom metal plates of the superposed metals are superplastically molded, movement of the top and bottom plates is controlled by the auxiliary plates pressed from behind, whereby generation of wrinkles on the molded product can be prevented by avoiding local expansion generated in the no-bonding regions of the metal plates.
In the above-mentioned processes for the monolithic molding of superplastic material, the anti-bonding agent is preferably coated onto outer surfaces (i.e., free surfaces) of the auxiliary plates for molding. According to the invention, the auxiliary plates used for control of shape of the metal plates on the molding can be easily removed from the molding die, whereby the processing of the molding is enhanced in efficiency.
A further invention to attain the object is provided by a process for the monolithic molding of superplastic material comprising the steps of:
providing at least three metal plates capable of superplastic molding and diffusion bonding,
applying an anti-bonding agent onto regions of the plates to define bonding regions and non-bonding regions on the plates, bonding regions and non-bonding regions provided between the plates,
superposing the metal plates one on another to form superposed plates,
setting the superposed plates in a molding die, and
superplastically molding the metal plates by introducing a gas into the non-bonding regions to apply pressure to the regions;
wherein a groove connecting an end portion of one plate of the superposed plates (face sheet or core sheet) to one of the non-bonding regions is provided on the one plate, a stainless steel pipe having no superplastcicity is fitted into the groove, periphery of the pipe is sealed, all the plates constituting the superposed plates are superposed one on another and pressure is applied by introducing an insert gas into the stainless steel tube.
A groove (passage) directly provided on the face sheet or the core sheet is reduced in the diameter by pressure and heat (high temperature) of jig to increase resistance, and therefore time period for feeding molding gas is made longer. According to the above invention, the passage is not reduced in the dimension by fitting the stainless pipe into the passage and hence the feeding molding gas is not inhibited.